A spectrometer is an optical device for spectrally separating light, an object of measurement, into spectral components using dispersing elements such as prisms or diffraction gratings. By detecting the spectral components of light separated with the dispersing elements, the wavelength distribution of the light or the intensity of specific wavelength component of the light can be found out. Thus, spectrometers are used in a variety of application areas (for example, See Document 1: JP-A-2000-298066, Document 2: JP-A-Hei-4-294223, Document 3: JP-A-2000-65642).